In the past, a magnetic recording medium which is prepared by dispersing ferromagnetic particles such as .gamma.-Fe.sub.2 O.sub.3, Co-containing iron oxide, chromium dioxide or ferromagnetic alloy particles in a binder, and coating the thus obtained dispersion on a non-magnetic support to provide a magnetic layer has been used as a magnetic recording medium for audio recording, video recording and for computers in the shape of a tape or a disk. Recently, in order to realize high density recording and high S/N (signal/noise) ratio of such magnetic recording medium, the magnetic particles have been finely divided. However, with the tendency to make the magnetic particles finer and finer, the abrasive property of the magnetic particles is reduced, thereby resulting in a deterioration of the running durability of the magnetic recording medium using the above magnetic particles. This tendency is more striking when ferromagnetic alloy particles having a low hardness are employed.
In order to prevent the deterioration of running durability, it is proposed in U.S. Pat. No. 3,833,412 to add abrasive agents such as granular Al.sub.2 O.sub.3, SiC or Cr.sub.2 O.sub.3, to the magnetic layer. However, when a large amount of these abrasive agent is added, the magnetic orientation of the magnetic recording medium, the packing density of the magnetic particles and the dispersibility thereof are deteriorated, whereby the electromagnetic properties are deteriorated due to the deterioration of the surface property (i.e., surface smoothness).
When the added amount of the abrasive agents is reduced to improve the surface property, the electromagnetic properties are improved, but the running property of a magnetic recording medium is deteriorated because the friction coefficient of the magnetic layer increases, thereby leading to sticking between the magnetic head and the magnetic layer during running.
In order to resolve the above described problem, the inventors of the present invention proposed in Japanese Patent Appliction No. 62938/85 (corresponding to U.S. patent application Ser. No. 843,973 filed on Mar. 25, 1986) that acicular inorganic substance having an average length in the long axis of 1.0 .mu.m or less, an average length in the short axis of 0.1 .mu.m or less, a acicular ratio (long axis/short axis) of 5 to 20 and a Mohs' hardness of 5 or more be used as an abrasive agent. However, a satisfactory magnetic recording medium still has not been obtained.